Measles remains a major worldwide health problem. The primary complications associated with this infection are pneumonia, which may progress to chronic pulmonary disease, diarrhea, and post infectious encephalomyelitis, which is often associated with permanent neurologic damage. Previous studies have shown that mitogen-induced lymphoproliferative responses are depressed for 4-6 weeks after the onset of the rash and there is reason to believe that the effect of this viruls infection on th immune system of the infected individual may play a prominant role in the development of these complications. The objective of this proposal is to further define the relationship between measles virus infection and functional alterations in the immune system. To this end the types of cells and state of activation of mononuclear cells circulating in the peripheral blood of patients with measles at various times after infection will be determined using monoclonal antibodies for immunoperoxidase staining of cytocentrifuged cells. Monocytes from individuals with and without measles and uninfected and infected U937 cells will be tested for production of IL-1, interferon and prostaglandin as well as ability to supply accessory cell activity for mitogen-induced lymphoproliferation. Lymphocytes from individuals with and without measles will be tested for production of Il-2, -interferon, and the Tac antigen (IL-2 receptor) in response to mitogen stimulation.